Trigger Finger

Anatomy

The flexor tendons connect the digits to the forearm muscles and are responsible for bending the digits. A membranous tendon sheath covers the outside of the tendon and is attached to the bones of the hand, starting at the metacarpal head (palm bone) and extending to the distal phalanx (last finger bone). Different areas of the tendon sheath are thickened and function as pulleys to direct the tendon in its path and to prevent bowstringing. Trigger finger occurs when there is a mismatch in size of the flexor tendon, most commonly caused by a nodule, and the pulley. The most common area for the tendon to get stuck at is the first annular (A1) pulley, located over the joint of the metacarpal (palm bone) and proximal phalanx (initial finger bone). Occasionally, triggering can occur at other pulley sites.

Causes

Trigger finger is often idiopathic. It does occur more commonly in people with metabolic problems such as diabetes mellitus and hypothyroidism and different rheumatologic conditions, including rheumatoid arthritis, psoriatic arthritis, amyloidosis, sarcoidosis, and pigmented villonodular synovitis. Interestingly, trigger finger is associated with duration of diabetes and not with sugar control in individuals with diabetes requiring insulin injection. Because repetitive finger movements due to one's occupation or sport can cause high tension across the A1 pulley, it is proposed to cause the development of fibrocartilaginous metaplasia of the pulley and tendon cells, thus creating the mismatch in size. Trigger finger commonly coexists with carpal tunnel syndrome, de Quervain tenosynovitis, and Dupuytren contracture. Sometimes, locking of the digit can occur if ligaments catch on the bony prominence of the metacarpal (palm bone) head, if there is swelling of the tendon at different locations, or if loose bodies are present in the metacarpal phalangeal joint. Rarely, a finger injury involving a laceration of the flexor tendon may present as a trigger finger from the cut portion of the tendon catching at the A1 pulley.

Symptoms

Initially, pain is only felt in the palm at the metacarpal phalangeal joint. The pain can also radiate along the palm or along the digit. Locking of the digit occurs during active flexion-extension activities, often reported to worsen on rising in the morning. The athlete may complain initially of painless clicking of the digit with flexion that progresses to painful catching. Long-standing cases of [Page 1509]trigger finger may present as a stiff digit, which the person is unable to bend.

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